Since recently it is known that certain substances that may be present in the body can function as indicators for various pathological conditions in the body. Such substances are hereafter called indicator substances. Examples of indicator substances are glucose, lactate, pyruvate, glycerol, glutamate, and glutamine and heart specific enzymes. Pathological conditions that may be indicated or detected, or as well forecasted, include ischemia, hypoglycemia sepsis, cell membrane damage or lipolysis, vasospasms and metabolic disorders. By measuring indicator substances, pathological conditions may be detected before they lead to clinical signs. It may even be possible to detect processes or conditions that eventually may lead to a pathological condition. In many cases it would be advantageous to have the possibility to measure the concentration of indicator substances directly in a blood stream, or in tissue fluid. Systems known from the background art all have different drawbacks. Examples of common drawbacks in background art systems are that the measurement delay is extensive and that one has measured phenomena that are the result of a pathological condition, e.g. ischemia. This is clearly disadvantageous. With measurement delay is meant the time that passes from the moment that a sample is taken until the moment that a measurement value relating to this sample is obtained. In background art systems measurement values can often only be obtained with relatively extended time periods. In intensive care, blood gas sample are taken on the patients as often as once every hour, however, changes in the amounts of certain substances present in the blood could happen much more rapidly than this and immediate detection is advantageous for resolving the situation and balancing the levels of the substances rapidly. In intensive care patients, the monitoring of the physiological and biochemical state is crucial.
The process of taking an arterial blood gas, in accordance with the background art, starts with the step of collecting a blood sample from an artery of the patient. The radial artery is most commonly used because of its accessibility, its ability to constrict if a bleeding occurs and since the risk of occlusion is small in the radial artery. Alternatively arteries are for example the femoral artery and the brachial artery. The femoral artery is easy to find in an acute situation, but is a larger artery, which increases the risk of complications, such as bleedings. First, the area of the skin needs to be disinfected with a disinfecting solution. Then the pulse is palpated to find a part of the artery where the pulse feels strong and where it will be easy to find it with the needle. For entering the artery, a syringe with a thin removable needle is used. The syringe contains small amounts of heparin (anticoagulants) to prevent the blood from coagulating. The needle is pricked through the skin close to your finger where the pulse is palpable and is inserted until the artery is found. Sometimes this step is difficult and repeated attempts could be necessary. When the needle hits the artery the syringe starts to fill by itself. When the syringe is fully filled the needle is separated from the syringe. A special cap is put on the syringe to prevent the syringe from leaking blood. The sample is immediately labeled. It is important that there are no air bubbles in the syringe, since it could affect the result of the analysis. Immediately thereafter the sample needs to be sent to a laboratory for analyze.
For frequently repeated blood gas sampling, such as for patients in the intensive care units, it is easier to have an arterial catheter or an arterial line, which somewhat reduces the time of obtaining a sample and the amount of times that a patient needs to be pricked. The arterial line is most often inserted into the radial artery. When a blood sample is needed a syringe is placed in the arterial catheter to collect blood. Then the syringe is then taken to a blood gas analyzer. Intensive care units usually have a blood gas analyzer located centrally in the unit. The results from the blood gas analysis are usually available after five minutes. Since a unit usually treats several patients, the blood gas procedure takes up a substantial amount of the operative staff's time. Arterial blood is usually extracted by doctors or nurses with special skills in phlebotomy.
Arterial blood gas tests, in accordance with the background art, as disclosed above, are most commonly used in the emergency room, the emergency departments and in the intensive care units. Amongst other things, it is used for acid-base balance, i.e. pH measurement, partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2) and bicarbonate level. Many blood gas analyzers will also measure lactate, glucose, hemoglobin, bilirubin and electrolytes. The pH value of the blood is an indicator of the interaction between the blood, the renal- and the respiratory system.
There are many different situations in which it is important with an arterial blood gas analyze, for example, patients with respiratory syndromes, diabetes, intoxications, kidney diseases, infections and carbon monoxide poisoning.
The systems of the background art have a several drawbacks. The formation of gas bubbles in the syringe may result in inaccurate results; the sample from a plastic syringe needs to be analyzed within 30 minutes, which hinders the operative staff from collecting a multiplicity of samples before analyzing. The process of a single blood gas analysis takes about ten minutes. Furthermore the tests are not taken frequently enough to detect sudden changes in the condition of the patient. Last but not least contact with blood is always creates risks of spreading various deceases.